Preparation of synthetic rubber latices



Patented Sept. 13, 1949 UNITED STATES PATENT OFFICE" amass U. Glasgow-New York. N. Ytasalgnor to United States Rubber Company. New Yo N. Y., a corporation of New Jersey v No Drawing. Application April 21, 1948, Serial No. 22.500

This invention relates to an improvement in the process for the preparation of synthetic rubber latices. s. It is known that the viscosity of synthetic rubber latices depends upon the amount of synthetic rubber in the latex-the higher the solids content of the latex, the greater the viscosity. It is diillcult to produce high solids synthetic rubber latices, i; e. latices having over 45% so]- ids concentration directly in the reactor since the viscosity of the latex increasesto the point where stirring of the reactor batch is lnefllcient and heat transfer from the reactor batch to the reactor jacket is poor, whereby control of the polymerization is lost. Also the high viscosity 01' such synthetic rubber laticesat room temperature unduly restricts their use in processes requiring direct application of such latices.

I have found that the viscosity of a synthetic rubber latex produced by emulsion polymerization is greatly reduced if the polymerization is carried out in the presence of an acyiated casein. and that consequently such synthetic rubber latices may be satisfactorily prepared with a much higher solids content than in conventional synthetic rubber practice.

According to the present invention, the synthetlc rubber latex is prepared by polymerizing the aqueous emulsion of polymerizable monomers in the presence of a small amount of an acyiated casein. Acylated caseins, as is known,

may be prepared by the reaction of fatty acid anhydrides' or fatty acid chlorides on casein (Ind. ll E118. Chem., Ind. Ed-, V01. 38, D8865 90-94; 1239-1243), The acylbontent may be from 2 to 25% of anacylatedcasein product. The acyiating agent may be the anhydride or chloride fatty acids having 2 to 18 carbon atoms. For

example. one may use, according to the preslnvention.=;the acetyl propionyl, butyryl, camy e'apr lyl. .pelargonyl, capryl, lauroyl, I myristoyl,

toyl, oleoyl, or stearoyl derivacording to the present invention, is conventional except for the presence of the small amount of acyiated casein which reduces the viscosity of the synthetic rubber latex and permits the preparation of higher, soiids content latices, The

amount of acylated casein may be from .05 to .8 part by weight per 100 parts of poiymerizable oclalms. (Cl. 280-8) monomers. Over .5 part of acyiated casein per 100 parts of polymerizable monomers has a tendency to destabilize the latex and form flocculated particles. The present invention may be used in the preparation of synthetic-rubber latex having a, total solids content, e. g. in preparing conventional 25% to 45% solids concentration latices having greatly lowered viscosities," and in preparing synthetic rubber latices having solids concentrations above 45% up to 60%, which are very difllcult, if not almost impossible to prepare by conventional commercial procedures. The acyiated casein is preferably added to'the initial emulsion of polymerizable monomers in order to obtain the maximum advantage of the acyiated casein, but if desired, the acyiated casein may be added at a later stage of the polymerization before one-half the final polymerization :has

, 2,3-dimethylbutadiene-1,3.

taken place so that in any cases major proportion of the desired polymerization of the polymerizable monomers is carried out in the presence of the acyiated casein.

In the preparation of the synthetic rubber latex, as is known, polymerizable monomeric compounds are emulsified in water with the aid of an emulsifying agent, such as a soa or other surface active agent, and the polymerization is made to take place generally at elevated temperatures in the presence of a catalyst andother regulating materials. Such polymerizable material may be one or a mixture of butadiene-1,3 hydrocarbons, for example, butadiene 1,3, methyl-2-butadiene-l,3 (isoprene), piperylene, The polymerizable material as is known may be a mixture of one or more of such butadiene-.1,3 hydrocarbons with one :or more other polymerizable compounds which are capable of forming rubbery copolymers withbutadiene-1,3 hydrocarbons, for example, up to 70% of such mixture of one or more compounds which contain 'a single CHg=C group where at least oneof-the disconnectedvalences is attached to an elect; rregative group, that is, a group which substa' aily'lincreases the electrical dissymmetry o'r polar c I aracter of the molecule. Examples of compounds whichps; contain a CHa==C group and are co polynierizable'= with butadienes-l,3 are aryiolefins, such as styrene, and vinyl naphthalene; .the' alpha methylene .carboxylic acids, and theirfesters, .n'itriles and amides, ,such as acrylic acid. methyl acrylate, methyl methacrylate, acrylonitrile, methacrylo- 4 nitrile, fmethacrylamidej; methyl vinyl ether:

methyljvinyl ketone; vinylidene chloride.

The following examples are(illustrative. of 213118 inyention, all parts-referredto thereinbeing .by

weisht:

' or flocculated particles.

oneness Example I A reactor batch of an aqueous emulsion of a mixture or butadiene and styrene was made according to the following iormulatlon:

'ifi'he caprylyl content or the caprylyl casein was about The caprylyl casein and dodecyl mercaptan (regulator) were added to the styrene, which was in turn added to the aqueous solution oi the sodium abietate (soap emulsifying agent), sodium hydroxide (stabilizer). and potassium persulfate (catalyst) in the-reactor vessel. The butadiene was finally added to the reactor batch and polymerization was carried out at 45 with continuous agitation for 60. hours. The conversion of monomers to polymer was 95%. giving a 55% solids content latex having a viscosity between 100 and 200 centipoises and free from coagulum Without the caprylyl casein, the latex is more viscous and contains considerable coagulum and fiocculated particles.

Example I] An aqueous emulsion of polymerizable monomers similar to Example I but with .25 part of lauroyl casein (lauroyl content about as the acylated casein, was prepared according to the following formulation:

Polymerization was carried out at 45 C. with continuous agitation for 50 hours, giving a conversion of monomers to polymer of 95%. The final synthetic rubber latex had a total solids content of over 55%. and a viscosity between 100 prises carrying out the emulsion polymerization in the presence of .05 to .5 part by weight otacylated casein.; the acyl groups being fatty acid ari-groups. mparts oi'polymerm le mon- 1 2. The improvement inthe process for the preparation of synthetic rubber latex by the emulsion polymerization with a soap emulsifying" agent of poiymerizable' monomers selected from the group consisting o'i' b'utadienes-Lii and mixtures 01' butadien'es-L3 with compounds which contain a single cH==C group and are copolymerizable with butadienes-1,3 which comprises carrying out at least a major proportion of the emulsion polymerization in the presence of .05 to .5 part by weight 0! acylated casein. the acyl groups being fatty acid acyl groups. per 100 parts of polymerizabie monomers.

3. The improvement in'the process ,tor the preparation or synthetic. rubber latex having 45 to 80% solids concentration by the emulsion polymerization with a soap emulsifying agent of polymerizable monomers selected from the group consisting of butadlenes-1,3 and mixtures of butadienes-L3. with compounds which contain a single CH2=C group and are copolymerizable with butadienes-1.3 which comprises carrying out at least a-maior proportion oi the and 200 centipoises without coagulum or flocculated particles. Without the lauroyl casein, the

iinal latex is much more viscous and contains considerable flocculated particles. 11' ordinary casein is substituted for the acylated casein in the above examples. latices containing large amounts of coagulum result.

In view of the many changes and modifications that may be made without departing from the principles underlying the invention, reference should be made to the appended claims for an understanding of the scope oi the protection agorded the invention.

jl i aving thus described my invention. what I claim and desire to protect by Letters Patent is:

1. The improvement in the process for the preparation of synthetic rubber late: by the emulsion polymerization with a soap emulsifying agent of polymerizable monomers selected from the group consisting of butadienes-L3 and emulsion polymerization in the presence of .05" to .5 partby weight 01' acylated casein, the acyl groups being fatty acid acyl groups. per parts of polymerizable monomers.

4. The improvement in the process for the preparation of synthetic rubber latex by the emulsion polymerization with a soap emulsifying agent of a mixture or butadiene-ha and styrene which comprises carrying out the emulsion polymerization in the presence or .05 to 5 part by weight of acylated casein. the acyl groups being fatty acid acyl groups. per 100 parts at polymerizable monomers. 1

5. The improvement in the process for the preparation of synthetic rubber latex by the emulsion polymerization with a soap emulsifying agent or a mixture of butadiene-1,3 and styrene which comprises carrying out at, least a major proportion of the emulsion polymerization in the presence of .05 to .5 part by weight of acylated casein, the acyl groups being fatty acid acyl groups, per 100 parts of polymerimble monomers.

6. The improvement in the process for the preparation of synthetic rubber latex having-45 to -60% solids concentration by the emulsion polymerization with a soap emulsifying agent of a mixture or butadiene-l,3 and styrene which comprises carrying out at least a major proportion or the emulsion polymerization in the presence of .05 to .5 part by weight of acylated The following references are of record in the his or this patent:

UNITED STATES PATENTS Name Date Becker Feb. 15, 1938 OTHER REFERENCES Gordon et al.'. Ind. Eng. Chem. vol. as, c ses mas-i242. (Copy in Scientific Library.) j

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